Increasing regulatory and operational pressure has resulted in the need for hydrocarbons that have low sulfur levels and nitrogen levels. Hydroprocessing, which involves treating a hydrocarbon with hydrogen in the presence of a catalyst, is a conventional method for heteroatom (e.g., sulfur and nitrogen) removal.
Conventional hydroprocessing (i.e., known to those skilled in the art of hydrocarbon upgrading) catalysts generally contain a Group VIB metal with one or more Group VIII metals on a refractory support. Hydrotreating catalysts that are particularly suitable for hydrodesulfurization, as well as hydrodenitrogenation, generally contain molybdenum or tungsten on alumina promoted with a metal such as cobalt, nickel, iron, or a combination thereof. Cobalt promoted molybdenum on alumina catalysts are most widely used when the limiting specifications are hydrodesulfurization, while nickel promoted molybdenum on alumina catalysts are the most widely used for hydrodenitrogenation, partial aromatic saturation, as well as hydrodesulfurization.
PCT Publication WO 00/41810 describes bulk catalyst compositions comprising bulk catalyst particles having at least one group VIII metal and at least two group VIB metals (hereafter referred to as trimetallic bulk catalysts), in particular nickel/molybdenum/tungsten based catalysts. The trimetallic bulk catalyst particles are prepared in a process in which the metal components are combined in the presence of a protic liquid and wherein one or more metal components remains at least partly in the solid state during the entire process, i.e., a solid-solute process. The patent publication also describes in the comparative examples a bimetallic bulk catalyst comprising one Group VIII metal and only one Group VIB metals prepared with the solid-solute process.
Although WO 00/41810 describes wide ranges for the metal molar ratio, acceptable conversions are achieved only at a metal molar ratio above 1.25. As too high a metal molar ratio may add unnecessary weight and reduce the activity per unit weight of the bulk catalyst, there is a need for bulk catalysts having a high activity and a reduced metal molar ratio, i.e., a reduced amount of Group VIII promoter metal.